class Gtk::Builder

• Gtk::Builder
• GObject::Object
• Reference
• Object

Overview

Reads XML descriptions of a user interface and instantiates the described objects.

To create a Gtk::Builder from a user interface description, call Gtk::Builder#new_from_file, Gtk::Builder#new_from_resource or Gtk::Builder#new_from_string.

In the (unusual) case that you want to add user interface descriptions from multiple sources to the same Gtk::Builder you can call Gtk::Builder.new to get an empty builder and populate it by (multiple) calls to Gtk::Builder#add_from_file, Gtk::Builder#add_from_resource or Gtk::Builder#add_from_string.

A Gtk::Builder holds a reference to all objects that it has constructed and drops these references when it is finalized. This finalization can cause the destruction of non-widget objects or widgets which are not contained in a toplevel window. For toplevel windows constructed by a builder, it is the responsibility of the user to call Gtk::Window#destroy to get rid of them and all the widgets they contain.

The functions Gtk::Builder#object and Gtk::Builder#objects can be used to access the widgets in the interface by the names assigned to them inside the UI description. Toplevel windows returned by these functions will stay around until the user explicitly destroys them with Gtk::Window#destroy. Other widgets will either be part of a larger hierarchy constructed by the builder (in which case you should not have to worry about their lifecycle), or without a parent, in which case they have to be added to some container to make use of them. Non-widget objects need to be reffed with g_object_ref() to keep them beyond the lifespan of the builder.

Gtk::Builder UI Definitions

Gtk::Builder parses textual descriptions of user interfaces which are specified in XML format. We refer to these descriptions as “Gtk::Builder UI definitions” or just “UI definitions” if the context is clear.

Structure of UI definitions

UI definition files are always encoded in UTF-8.

The toplevel element is <interface>. It optionally takes a “domain” attribute, which will make the builder look for translated strings using dgettext() in the domain specified. This can also be done by calling Gtk::Builder#translation_domain= on the builder. For example:

WARNING ⚠️ The following code is in xml ⚠️

<?xml version="1.0" encoding="UTF-8">
<interface domain="your-app">
  ...
</interface>

Requirements

The target toolkit version(s) are described by <requires> elements, the “lib” attribute specifies the widget library in question (currently the only supported value is “gtk”) and the “version” attribute specifies the target version in the form “<major>.<minor>”. Gtk::Builder will error out if the version requirements are not met. For example:

WARNING ⚠️ The following code is in xml ⚠️

<?xml version="1.0" encoding="UTF-8">
<interface domain="your-app">
  <requires lib="gtk" version="4.0" />
</interface>

Objects

Objects are defined as children of the <interface> element.

Objects are described by <object> elements, which can contain <property> elements to set properties, <signal> elements which connect signals to handlers, and <child> elements, which describe child objects.

Typically, the specific kind of object represented by an <object> element is specified by the “class” attribute. If the type has not been loaded yet, GTK tries to find the get_type() function from the class name by applying heuristics. This works in most cases, but if necessary, it is possible to specify the name of the get_type() function explicitly with the "type-func" attribute. If your UI definition is referencing internal types, you should make sure to call g_type_ensure() for each object type before parsing the UI definition.

Objects may be given a name with the “id” attribute, which allows the application to retrieve them from the builder with Gtk::Builder#object. An id is also necessary to use the object as property value in other parts of the UI definition. GTK reserves ids starting and ending with ___ (three consecutive underscores) for its own purposes.

Properties

Setting properties of objects is pretty straightforward with the <property> element: the “name” attribute specifies the name of the property, and the content of the element specifies the value:

WARNING ⚠️ The following code is in xml ⚠️

<object class="Gtk::Button">
  <property name="label">Hello, world</property>
</object>

If the “translatable” attribute is set to a true value, GTK uses gettext() (or dgettext() if the builder has a translation domain set) to find a translation for the value. This happens before the value is parsed, so it can be used for properties of any type, but it is probably most useful for string properties. It is also possible to specify a context to disambiguate short strings, and comments which may help the translators:

WARNING ⚠️ The following code is in xml ⚠️

<object class="Gtk::Button">
  <property name="label"
            translatable="yes"
            context="button"
            comments="A classic">Hello, world</property>
</object>

The xgettext tool that is part of gettext can extract these strings, but note that it only looks for translatable="yes".

Gtk::Builder can parse textual representations for the most common property types:

• characters
• strings
• integers
• floating-point numbers
• booleans (strings like “TRUE”, “t”, “yes”, “y”, “1” are interpreted as true values, strings like “FALSE”, “f”, “no”, “n”, “0” are interpreted as false values)
• string lists (separated by newlines)
• enumeration types (can be specified by their full C identifier their short name used when registering the enumeration type, or their integer value)
• flag types (can be specified by their C identifier or short name, optionally combined with “|” for bitwise OR, or a single integer value e.g., “GTK_INPUT_HINT_EMOJI|GTK_INPUT_HINT_LOWERCASE”, or “emoji|lowercase” or 520).
• colors (in the format understood by Gdk::RGBA#parse)
• transforms (in the format understood by Gsk::Transform#parse)
• Pango attribute lists (in the format understood by Pango::AttrList#to_string)
• Pango tab arrays (in the format understood by Pango::TabArray#to_string)
• Pango font descriptions (in the format understood by Pango::FontDescription#from_string)
• GVariant (in the format understood by GLib::Variant#parse)
• textures (can be specified as an object id, a resource path or a filename of an image file to load relative to the Builder file or the CWD if Gtk::Builder#add_from_string was used)
• GFile (like textures, can be specified as an object id, a URI or a filename of a file to load relative to the Builder file or the CWD if Gtk::Builder#add_from_string was used)

Objects can be referred to by their name and by default refer to objects declared in the local XML fragment and objects exposed via Gtk::Builder#expose_object. In general, Gtk::Builder allows forward references to objects declared in the local XML; an object doesn’t have to be constructed before it can be referred to. The exception to this rule is that an object has to be constructed before it can be used as the value of a construct-only property.

Child objects

Many widgets have properties for child widgets, such as Gtk::Expander#child. In this case, the preferred way to specify the child widget in a ui file is to simply set the property:

WARNING ⚠️ The following code is in xml ⚠️

<object class="Gtk::Expander">
  <property name="child">
    <object class="Gtk::Label">
    ...
    </object>
  </property>
</object>

Generic containers that can contain an arbitrary number of children, such as Gtk::Box instead use the <child> element. A <child> element contains an <object> element which describes the child object. Most often, child objects are widgets inside a container, but they can also be, e.g., actions in an action group, or columns in a tree model.

Any object type that implements the Gtk::Buildable interface can specify how children may be added to it. Since many objects and widgets that are included with GTK already implement the Gtk::Buildable interface, typically child objects can be added using the <child> element without having to be concerned about the underlying implementation.

See the Gtk::Widget documentation for many examples of using Gtk::Builder with widgets, including setting child objects using the <child> element.

A noteworthy special case to the general rule that only objects implementing Gtk::Buildable may specify how to handle the <child> element is that Gtk::Builder provides special support for adding objects to a Gio::ListStore by using the <child> element. For instance:

WARNING ⚠️ The following code is in xml ⚠️

<object class="GListStore">
  <property name="item-type">MyObject</property>
  <child>
    <object class="MyObject" />
  </child>
  ...
</object>

Property bindings

It is also possible to bind a property value to another object's property value using the attributes "bind-source" to specify the source object of the binding, and optionally, "bind-property" and "bind-flags" to specify the source property and source binding flags respectively. Internally, Gtk::Builder implements this using GObject::Binding objects.

For instance, in the example below the “label” property of the bottom_label widget is bound to the “label” property of the top_button widget:

WARNING ⚠️ The following code is in xml ⚠️

<object class="Gtk::Box">
  <property name="orientation">vertical</property>
  <child>
    <object class="Gtk::Button" id="top_button">
      <property name="label">Hello, world</property>
    </object>
  </child>
  <child>
    <object class="Gtk::Label" id="bottom_label">
      <property name="label"
                bind-source="top_button"
                bind-property="label"
                bind-flags="sync-create" />
    </object>
  </child>
</object>

For more information, see the documentation of the GObject::Object#bind_property method.

Please note that another way to set up bindings between objects in .ui files is to use the Gtk::Expression methodology. See the Gtk::Expression documentation for more information.

Internal children

Sometimes it is necessary to refer to widgets which have implicitly been constructed by GTK as part of a composite widget, to set properties on them or to add further children (e.g. the content area of a Gtk::Dialog). This can be achieved by setting the “internal-child” property of the <child> element to a true value. Note that Gtk::Builder still requires an <object> element for the internal child, even if it has already been constructed.

Specialized children

A number of widgets have different places where a child can be added (e.g. tabs vs. page content in notebooks). This can be reflected in a UI definition by specifying the “type” attribute on a <child> The possible values for the “type” attribute are described in the sections describing the widget-specific portions of UI definitions.

Signal handlers and function pointers

Signal handlers are set up with the <signal> element. The “name” attribute specifies the name of the signal, and the “handler” attribute specifies the function to connect to the signal.

WARNING ⚠️ The following code is in xml ⚠️

<object class="Gtk::Button" id="hello_button">
  <signal name="clicked" handler="hello_button__clicked" />
</object>

The remaining attributes, “after”, “swapped” and “object”, have the same meaning as the corresponding parameters of the GObject::signal_connect_object or GObject::signal_connect_data functions:

• “after” matches the G_CONNECT_AFTER flag, and will ensure that the handler is called after the default class closure for the signal
• “swapped” matches the G_CONNECT_SWAPPED flag, and will swap the instance and closure arguments when invoking the signal handler
• “object” will bind the signal handler to the lifetime of the object referenced by the attribute

By default "swapped" will be set to "yes" if not specified otherwise, in the case where "object" is set, for convenience. A “last_modification_time” attribute is also allowed, but it does not have a meaning to the builder.

When compiling applications for Windows, you must declare signal callbacks with the G_MODULE_EXPORT decorator, or they will not be put in the symbol table:

WARNING ⚠️ The following code is in c ⚠️

G_MODULE_EXPORT void
hello_button__clicked (Gtk::Button *button,
                       gpointer data)
{
  // ...
}

On Linux and Unix, this is not necessary; applications should instead be compiled with the -Wl,--export-dynamic argument inside their compiler flags, and linked against gmodule-export-2.0.

Example UI Definition

WARNING ⚠️ The following code is in xml ⚠️

<interface>
  <object class="Gtk::Dialog" id="dialog1">
    <child internal-child="content_area">
      <object class="Gtk::Box">
        <child internal-child="action_area">
          <object class="Gtk::Box">
            <child>
              <object class="Gtk::Button" id="ok_button">
                <property name="label" translatable="yes">_Ok</property>
                <property name="use-underline">True</property>
                <signal name="clicked" handler="ok_button_clicked"/>
              </object>
            </child>
          </object>
        </child>
      </object>
    </child>
  </object>
</interface>

Using Gtk::Buildable for extending UI definitions

Objects can implement the Gtk::Buildable interface to add custom elements and attributes to the XML. Typically, any extension will be documented in each type that implements the interface.

Menus

In addition to objects with properties that are created with <object> and <property> elements, Gtk::Builder also allows to parse XML menu definitions as used by Gio::Menu when exporting menu models over D-Bus, and as described in the Gtk::PopoverMenu documentation. Menus can be defined as toplevel elements, or as property values for properties of type GMenuModel.

Templates

When describing a Gtk::Widget, you can use the <template> tag to describe a UI bound to a specific widget type. GTK will automatically load the UI definition when instantiating the type, and bind children and signal handlers to instance fields and function symbols.

For more information, see the Gtk::Widget documentation for details.

Defined in:

Constructors

• .new : self

  Creates a new empty builder object.

• .new(*, current_object : GObject::Object | Nil = nil, scope : Gtk::BuilderScope | Nil = nil, translation_domain : String | Nil = nil)
• .new_from_file(filename : String) : self

  Parses the UI definition in the file filename.

• .new_from_resource(resource_path : String) : self

  Parses the UI definition at resource_path.

• .new_from_string(string : String, length : Int64) : self

  Parses the UI definition in string.

Class Method Summary

• .g_type : UInt64

  Returns the type id (GType) registered in GLib type system.

Instance Method Summary

• #==(other : self)

  Returns true if this reference is the same as other.

• #add_from_file(filename : String) : Bool

  Parses a file containing a UI definition and merges it with the current contents of builder.

• #add_from_resource(resource_path : String) : Bool

  Parses a resource file containing a UI definition and merges it with the current contents of builder.

• #add_from_string(buffer : String, length : Int64) : Bool

  Parses a string containing a UI definition and merges it with the current contents of builder.

• #add_objects_from_file(filename : String, object_ids : Enumerable(String)) : Bool

  Parses a file containing a UI definition building only the requested objects and merges them with the current contents of builder.

• #add_objects_from_resource(resource_path : String, object_ids : Enumerable(String)) : Bool

  Parses a resource file containing a UI definition, building only the requested objects and merges them with the current contents of builder.

• #add_objects_from_string(buffer : String, length : Int64, object_ids : Enumerable(String)) : Bool

  Parses a string containing a UI definition, building only the requested objects and merges them with the current contents of builder.

• #create_closure(function_name : String, flags : Gtk::BuilderClosureFlags, object : GObject::Object | Nil) : GObject::Closure | Nil

  Creates a closure to invoke the function called function_name.

• #current_object : GObject::Object | Nil

  Gets the current object set via gtk_builder_set_current_object().

• #current_object=(current_object : GObject::Object | Nil) : Nil

  Sets the current object for the builder.

• #expose_object(name : String, object : GObject::Object) : Nil

  Add object to the builder object pool so it can be referenced just like any other object built by builder.

• #extend_with_template(object : GObject::Object, template_type : UInt64, buffer : String, length : Int64) : Bool

  Main private entry point for building composite components from template XML.

• #hash(hasher)

  See Object#hash(hasher)

• #object(name : String) : GObject::Object | Nil

  Gets the object named name.

• #objects : GLib::SList

  Gets all objects that have been constructed by builder.

• #scope : Gtk::BuilderScope

  Gets the scope in use that was set via gtk_builder_set_scope().

• #scope=(scope : Gtk::BuilderScope | Nil) : Nil

  Sets the scope the builder should operate in.

• #translation_domain : String | Nil

  Gets the translation domain of builder.

• #translation_domain=(value : String) : String
• #translation_domain=(value : Nil) : Nil

  Set #translation_domain property to nil.

• #translation_domain=(domain : String | Nil) : Nil

  Sets the translation domain of builder.

• #translation_domain? : String | Nil

  Same as #translation_domain, but can return nil.

• #type_from_name(type_name : String) : UInt64

  Looks up a type by name.

• #value_from_string(pspec : GObject::ParamSpec, string : String) : GObject::Value

  Demarshals a value from a string.

• #value_from_string_type(type : UInt64, string : String) : GObject::Value

  Demarshals a value from a string.

Constructor Detail

Class Method Detail

Instance Method Detail